1. Field of the Invention
This invention generally relates to a linear motion rolling contact bearing assembly for providing a theoretically unlimited linear relative motion between a slider and a rail, and, in particular, to a linear motion rolling contact bearing assembly whose rolling contact resistance varies automatically depending on the magnitude of a load applied.
2. Description of the Prior Art
A linear motion rolling contact bearing assembly is well known in the art, and it generally includes a rail extending straight over a desired length, a slider which moves along the rail, and a plurality of balls interposed between the rail and the slider thereby providing a rolling contact between the slider and the rail. The slider is provided with at least one endless path, a part of which is defined as a load path section between the slider and the rail so that the balls located in this load section provide a rolling contact relation between the slider and the rail. Since the balls may circulate indefinitely along the endless path, theoretically, there may be provided an unlimited linear motion for the slider; however, in actuality, the linear motion of the slider is limited by the length of the rail provided.
Typically, the rail has a pair of side surfaces each of which is provided with a guide groove and the slider is provided with a pair of endless paths each of which defines a load section together with the corresponding one of the pair of guide grooves formed in the rail. That portion of the endless path which defines the load section is also in the shape of a groove which faces the corresponding groove of the rail to define a passage therebetween. Each of these grooves is normally so designed that each of the balls when located in the load section comes into contact at two points. Thus, each of the balls located at the load section normally has four contact points, i.e., two contact points with the groove of the rail and two contact points with the groove of the slider.
It is true that, if each of the balls has four contact points at the load section, it can withstand higher loads with less distortion. However, the larger the number of contact points, the higher the level of rolling contact resistance. This effect is multiplied if the number of the balls located in the load section increases. Thus, this may limit the application of linear motion rolling contact bearing assemblies to high speed applications and/or light load applications.